Catalyzed liquid reticulation of polyurethane foams



\ Jan. 21, 1969 R. G. SUTTON 3,423,338

CATALYZED LIQUID RETICULATION OF POLYURETHANE FOAMS Filed April 30. 1965C BENZYL ALCOHOL IO PARTS NcLOH PER 100 PARTS H1O, BENZYL ALCOHOL,ETHYLENE GLYCOL AT 25C.

Fig

H2O A B ETHYLENE GLYCOL C BENZYL ALCOHOL 2O PARTS NQOH PER 100 PARTS HO, BENZYL ALCOHOL, PROPYLENE GLYCOL AT 25C.

ATTORNEY United States Patent Claims Int. Cl. C08g 22/44 ABSTRACT OF THEDISCLOSURE Process for reticulating polyurethane foam at a temperaturebelow 50 C. by immersing a foam body in an aqueous solution of analkaline hydroxide, a water-soluble glycol, and a monocyclic aromaticalcohol.

This invention pertains to reticulation of polyurethane foams; morespecifically, this invention involves the use of novel liquids forreticulating polyurethanes such as polyester polyurethanes, polyetherpolyurethanes, polyether amine polyurethanes, etc.

Prior art methods for reticulating polyurethane foams can be dividedinto two groups. First, flame techniques have been used to obtain areticulated skeletonized polyurethan foam. Examples of such methods areexplosion reticulation and burning reticulation or melting reticulation.Second, catalyzed hydrolytic action on polyurethane foams has been usedto produce reticulated polyester polyurethane structures, and, to alesser degree, polyether and polyether-amine urethane structures.

By J r, the most popular hydrolytic reticulation has been et acted byusing sodium hydroxide-catalyzed water solutio. s on the polyesterpolyurethanes at about 10% sodiun hydroxide concentration and at about50 C. and hi her.

Various attempts have been made to accelerate this hydro tytic actionand these attempts have resulted in some impruvementsgenerally,improvement in the reaction rate.

Despite the improved reaction rate these processes have presenteddifferent and added problems in liquid reticulation. One has been theintroduction of high-vapor-pressure solvents in the solution. Forexample, British Patent 858,127, Example 3, shows the use of acetone asan aid in sodium hydroxide-catalyzed hydrolytic reticulation.Additionally, other processes have been disclosed in the patentliterature showing the use of monohydroxy glycol ethers as additives inalkaline solution-catalyzed hydrolytic reticulation.

Still other processes have illustrated additives such as alcohols inalkaline-catalyzed hydrolytic reticulation. In the last method,apparently, the alleged alkaline solutions are not true solutions withalcohols having more than two carbon atoms, i.e., methanol and ethanol.It has been found that propanol separates out of the alkaline solutionat the needed concentrations, and the catalyzed reaction is due to thealkaline solution with the propanol aiding perhaps only the contactingof foam with the sodium hydroxide solution. Therefore, true solutionsare exceptions in liquid reticulation and are only found in certain verylimited instances with methanol and ethanol and then only at verylimited conditions of alkaline concentrations.

Another approach in the catalyzed aqueous reticulation of polyurethanehas involved the use of halogensubstituted hydrocarbon in a mixture withalcohols and/ or phenols. This method, again, has been restricted tomethanols and ethanols and has, in very few limited instances, resultedin a true solution. In those cases where these solutions have separatedinto alcohol and aqueous phases the reticulation has been the result ofthe aqueous alkaline solution.

Still another method of liquid reticulation based on the alkalireticulation allegedly employs anhydrous methyl alcohol and hydrousalcohols such as methyl ethyl, propyl and butyl alcohols. Although inthis method the anhydrous alcohol is a starting material no mention hasbeen made of the concentration of the sodium hydroxide or the otherconstituents, and it can be inferred that this is not a truly anhydroussolution because neither solid sodium hydroxide nor solid potassiumhydroxide has been employed.

It has now been found that a superior combination of reactants canreticulate polyurethane foams under controlled conditions in a truesolution avoiding most of the problems of the higher vapor-pressureadditives employed in the prior art and at high reaction rates.

The present invention has been achieved by permeating a polyurethanefoam body with a reticulating solution comprised of (a) alkalihydroxides such as sodium and potassium hydroxides, (b) an aromaticalcohol, (0) water and (d) a glycol, for a time sufficient to achievereticulation and thereafter arresting the reaction by removing thereticulating solution from the polyurethane body or neutralizing andwashing the polyurethane body. In this combination of components glycolsappear to give the unexpected rate of reaction but more importantly theglycols allow the use of heretofore unachieved amounts of causticmaterial.

Properties of the obtained foam are somewhat closer to theexplosion-reticulated foam than to the liquid alkaline-reticulated foam.However, the differences between each of these are slight and within therange of experimental error, and therefore, for all practical purposesthese three types of foam are alike.

At this point it should be cautioned that permeatoidal degradation offoams of this invention may be prevalent if the reticulation conditionsare not carefully controlled. Therefore, in order to avoid thephenomenon of permeatoidal degradation, and also, uneven reticulation,the time of exposure of foam to the above solution, the temperature ofthe solution, and the relative proportions of the varius components mustbe controlled to obtain optimum results.

Generally, it has been found that temperatures below 45 C. arepreferred. The lower temperature limit is the freezing point and/ orphase separation which occurs near the freezing temperatures. The morepreferred temperatures are below 40 C. and are based on vapor-pressureconsiderations or the additional safety factors such as hot caustichandling including heating and corrosion. The most preferredtemperatures are from about 30 C. to about 25 C.

Because the reaction rate will double for every 10 C. temperature isvery important and should be held as constant as possible. However, inreticulating polyurethane foams with large pores, e.g., 5 p.p.i. foams(pores per lineal inch), high temperatures and longer immersion timesare needed such as about 5 minutes at about 45 C. for the 5 p.p.i..foam.At the other end of the foam structures for example, at about 125 poresper lineal inch and higher pore counts, the immersion times are veryshort and the temperatures are considerably lower, such as 35 C. andbelow.

To further illustrate the various relationships the following figureshave been included wherein:

FIGURE 1 shows a ternarydiagram of water, ethylene glycol and benzylalcohol with sodium hydroxide comprising 10 parts per parts of the threecomponents and the whole solution at 25 C. The area A, B, and C'represent the one-phase region of the solution giving uniform propertieswhen polyurethane foams such as polyester polyurethane foams aresubjected with this solution to reticulated conditions. Within theregion equal foam property temperature isotherms will be found. Ofcourse, the lower temperatures are the most preferred if equal propertycharacteristics may be obtained.

FIGURE 2 is a ternary diagram showing water, benzyl alcohol andpropylene glycol at 25 C. and at sodium hydroxide concentration of 20parts per 100 parts of the solution. The area A, B, and C represent theonephase region of the solution giving excellent results.

Polyurethane foams suitable for reticulation are well known in the artand the listing of the many ester, ether, polyether amine, etc., foamswould only be repetition of the by now well known foams. A number ofsuitable foams are mentioned in US. Patent 3,171,820. The polyesterfoams are preferred over others.

In general, all water soluble aromatic alcohols and all aromaticalcohols made water soluble by the glycol component are embraced withthe above term. However, for economical reasons the commerciallyavailable benzyl or mono cyclic aromatic alcohols such as guaiacol andresorcinol are preferred. The most preferred alcohol is benzyl alcoholwhich also gives the best results.

Glycols useful in the present reaction are generally those that aresoluble in at least 10% aqueous caustic solutions at room temperatures.Because the aromatic alcohols used are, as a general rule, insoluble inaqueous solution the quantity of glycol added is dependent upon the typeof alcohol applied. Also, as the quantity of sodium hydroxide of thealkaline material is increased, more ethylene glycol is required to keepthe alcohol in solution. As the temperature is increased the quantity ofglycol required is decreased. It is noted that when water is reduced toless than 10 parts of the total solution or lower, the Na hydroxidecrystallizes out of the solution when ethylene glycol is used. However,propylene glycol can tolerate considerably larger amounts of caustic.

Of the glycols employed those having from two to four carbon atoms arethe more preferred, such as ethylene glycol and propylene glycol andtheir water-soluble condensation products. The propylene glycol is mostpreferred. Because it is well known that glycols become lesswater-soluble with increase in molecular weight as well as increase incondensation, careful selection of the water soluble glycols isrequired. In addition, when the influence of alcohol on this waterglycol mixture is taken into consideration, it is evident that only avery specific relationship exists which allows proper reticulation ofpolyurethane foams.

By far the most common alkali agent useful in the present process issodium hydroxide and potassium hydroxide. Other alkali materials such asthe alkaline earth metal hydroxides are less dependable because of theirpoor solubility.

Although the discussion has been of hydrolytic action, it is not knownby what process the polyurethane reticulation reaction takes place. Itis believed, however, that there is an interaction of stress and anaccelerated highrate chemical reaction. This assumption or surmise isbased on the fact that the membranes removed from the polyurethane foamin the reticulation process fall out but apparently do not dissolve inthe solution.

It is believed that the membranes of polyurethane foam swell much morerapidly and that this difference in swelling places greater stressaround the edges of the membranes resulting in reticulation reaction.Comparatively speaking, the strands are essentially non-swelling at thepreferred reaction conditions. However, the foam does disintegrate inits component parts, in a relatively short time, e.g., about 5 minutesfor 45 p.p.i. polyester polyurethane foam at 35 C. in a sodiumhydroxidebenzyl alcohol-ethylene glycol solution.

The starting foam falls into nexus, strands attached to nexus andmembranes. Relatively very few individual strands are found in thesolution. It is believed that if the reaction were not stress-inducedand stress-accelerated a great number of strands would be found in thesolution because the stress-independent strands would be assumed todisintegrate at places joined to the nexus. Because of thestress-accelerated reaction the nexus and strands are joined together inthese assemblies. The disintegrated foam components stay suspended in itfor a long period of time, apparently without any further attack, andeven after three months the components are present in virtually the samedisintegrated form.

More surprisingly, in the present solutions, acids such as hydrochloric,sulphuric, etc., when used in place of caustic, result in no reaction.Moreover, not all of the expected polyurethane swelling solvents work inthe present solution when replacing either the alcohol or glycolcomponent. For example, the following chemicals were also evaluated inaqueous sodium hydroxide solution and the polyurethane foam wasimproperly reticulated due to immiscibility and/or very poor results:chlorinated solvents (immiscible, ether (immiscible), ketone(immiscible), hydroquinonels (no results) dimethyl acetamide (requireshigh temperatures and long reaction time), dimethyl formamide (hightemperatures, poor reticulation), dimethyl sulfoxide (high temperatures,poor reticulation). Even slight amounts of impurities will often slowdown the reaction or result in the separation of the present solution.This fact signifies that not all solutions which may appear acceptablewill function in the novel process.

As mentioned before, one unique advantage of this process is that thefoam is not discolored or matte-like. In fact, the product has theglossy appearance of an explosionor flame-reticulated foam. Generally,the strands remain very glossy and the color is enhanced. Besides, theweight loss of foams reticulated according to the novel methods is abouthalf of the weight loss encountered with hydrolitically reticulatedfoams such as according to the methods disclosed in US. 3,171,820.

The following examples are included to illustrate the invention.

Example 1 Reticulation process was carried out using 10 parts of sodiumhydroxide per 100 parts of the novel solution for various times and atvarious temperatures. The following solution was found to be verysuitable at lower temperatures: benzyl alcohol, 10%; water, 45%;ethylene glycol, 45%; sodium hydroxide, 10 parts per 100 parts of thesolution.

The polyester foam reticulated in the above solution was prepared by aconventional one-shot foaming process using /20 isomeric mixture of 2-4,2-6 toluene diisocyanate and Fomrez 50, an adipate polyester, which isreported to have a hydroxyl number of 51.8, and acid number of less than1.0 and a viscosity of 18,100 centipoises at 25 C. After curing, blockswere cut from the loaf and subjected to the above solution at 25 C. for15, 30 and 60 seconds, and after the stated time the reaction wasarrested by neutralizing the alkali with dilute solution of an acid suchas acetic acid and/ or by washing. 80-pore p.p.i. foam gave good resultsat 15 seconds and it was over reticulated at 30 seconds. 60 p.p.i. foamgave good results at 15 seconds, and it was over reticulated at 30seconds. 10 p.p.i. foam gave slight results at 15 seconds, good resultsat 30 seconds, and it was over reticulated at 60 seconds. A number oftests were conducted using the described foam and the solutionsillustrated on the ternary diagram in FIGURE 1.

Results classified as poor indicate that no apparent reticulation isevident but some windows have started to break.

Results classified as slight indicate that the foam is just beginning toreticulate, some membranes are broken, some are still attached to thestrands, and some are still unaffected.

Results classified as fair indicate that most of the membrane windowsare removed but about or more are present or attached to the strands.

Results classified as good indicate that there is a little edgeattachment of remaining membranes on the periphery of the strand butsubstantially all membranes are gone and the foam retains the glossyappearance of explosionor flame-reticulated foam.

Results classified as over reticulated indicate that the gloss presentin a good foam is gone and the compression/defiection propertiesdecrease in respect to a maximum value obtainable, i.e., foam becomessofter when compared to a properly reticulated sample.

In practicing the invention it is often advantageous to slightly workthe foam structure, such as by compressing and relaxing, to expel theentrapped air and bring the solution in contact with the membranousmatter. As can be envisioned, operating at 25 C. with solvent such asbenzyl alcohol is immeasurably safer than with methanol, ethanol, oracetone at higher temperatures.

Example 2 The same solution as used in Example 1 was used on an etherfoam at 30 C. prepared from 40 parts of Polyol 4025, which is a 4000molecular-weight diol derived from polypropylene oxide; 60 parts ofLHT-42, which is 4000 molecular-weight triol derived from polypropyleneoxide; 26.2 parts of toluene diisocyanate per 100 parts of the polyol;1.9 parts of water per 100 parts of the polyol mixture; 0.3 parts ofDabco per hundred parts of the polyol mixture (Dabco is a teriethylenediamine); 0.1 'part of triethylamine per hundred parts of the polyolmixture; and 0.3 part of D-22 per hundred parts of the polyl mixture (D-2'2 is a dibutyl tin dilaureate). These materials were mixed usingstandard urethane production procedures in a high-pressure polyurethanefoam-making machine. The foam mixture was allowed to free blow (underatmospheric conditions) and cured for at least 24 hours before handling.When compared with the results obtained with the ester foams of Example1 the ether foams are not as satisfactory as the ester foams.

Example 3 Foams of the same formulation as in Example 1 were reticulatedby the following two methods. First, a 10 solution of sodium hydroxideof 10 parts per 100 parts solution of 10% benzyl alcohol; 45% ethylenegylcol, and 45% water at 25 C. was employed to reticulate theabove-described ester foam. Second, a 20% solution of sodium hydroxideof 20 parts per 100 parts solution of 20% propylene gylcol; benzylalcohol and 65% water at 25 C. and 40 C. respectively was employed toreticulate the same foam. Results of the two reticulations were asfollows:

tions containing propylene glycol cause reticulations even more rapidlythan those solutions containing ethylene glycol.

Example 4 Instead of the regular free-blown polyurethane foam obtainedby allowing free expansion, compressed polyurethane foams containingmembranes with reticulated by means of the above solutions.

A polyester polyurethane foam of about 45 p.p.i. and of a thickness of/3 of its normal free-blown thickness obtained by compressingunreticulated foam (or alternatively by compressing blown green foam)was immersed in solutions illustrated in Example 3.

The immersed product was kept in the solution for a suflicient time toelfect reticulation. Upon removal from the solution and arresting of thereticulating reaction the foam was examined and observed to havesubstantially all of the Windows removed. However, it was noticed thatmany of the removed windows membranous matter) were still distributedloosely in the foam body.

This example demonstrates that this method is superior to some of theprior art methods which appear not to be able to effect satisfactoryreticulation of densified polyurethane foams.

Foams obtained according to the novel method were tested by ASTM methodD15 64-54T for compression/deflection, tear resistance, tensilestrength, elongation, compression set, aging resistance and solventresistance tests and compared favorably with the same polyurethane foamsreticulated by flame or explosive means and sodium hydroxide hydrolyticreticulation.

What is claimed is:

1. In the alkali-catalyzed method for reticulating polyurethane foams toobtain 3-dimensional reticulated structures of nexus and strands joinedto said nexus and substantially free from membranous matter, theimprovement comprising: immersing a membrane-containing polyurethanefoam body in a substantially true solution causing a reticulatingreaction, said solution being held at below 50 C., said solution beingcomprised of water, an alkaline hydroxide, a water-soluble glycol, and amonocyclic alcohol, said foam residing in said solution untilreticulation has been effected, separating said foam body from saidsolution and arresting the reticulating reaction.

2. In the alkali-catalyzed hydrolytic method for reticulatingpolyurethane foams to obtain a 3-dimensional reticulated structureconsisting of spaced-apart nexus and strands joined to said nexus andsubstantially free from membranous matter, the improvement comprising:immersing a membrane-containing polyurethane foam body in a reticulationreaction causing solution held at below 50 C., said solution comprisingan alkali metal hydroxide, water, a water-soluble glycol, and amonocyclic aromatic alcohol of from 7 to 10 carbon atoms, said foamresiding in said solution until reticulation has been effect-RETIOULATION RESULTS AT DIFFERENT IMMERSION TIMES AND TEMPERATURES 15seconds 30 seconds seconds Polyester foam Solution 1 Solution 2 Solution1 Solution 2 Solution 1 Solution 2 Norm-Solution 1 was not run at 40 C.

From the above it is amply evident that the novel solution offers vastlyfaster reaction rates so essential for modern day high velocityprocessing techniques. It is obvious from the data above that propyleneglycol solutions tolerate higher concentrations of caustic and thatover-reticulation of foam, while a problem with the particularsolutions, is not a problem when adequately diluted solutions are used."The above data also show that soluing a membrane-containing polyurethanefoam body in a reticulation reaction causing solution held at below 50C., said solution being comprised of sodium hydroxide, water, awater-soluble alkylene glycol of from 2 to 3 carbon atoms, and benzylalcohol, said foam residing in said solution until reticulation has beeneffected, separating said reticulated structure from said solution andarresting the reticulation reaction.

4. The process according to claim 3 wherein the glycol is ethyleneglycol.

5. The process according to claim 3 wherein the polyurethane ispolyester polyurethane.

6. A process according to claim 3 wherein the glycol is propyleneglycol.

7. A process according to claim 3 wherein the sodium hydroxide is 10parts per 100 parts of the solution.

8. The process according to claim 3 wherein the temperature is belowabout 30 C.

9. In the alkali-catalyzed hydrolytic method for reticulatingpolyurethane foam to obtain a 3-dimensional reticulated structureconsisting of spaced-apart nexus and strands joined to said nexus andsubstantially free from membranous matter, the improvement comprising:submerging a membrane-containing polyurethane foam body in 10 parts ofsodium hydroxide per 100 parts of mixture of water, benzyl, alcohol andethylene glycol solution, the proportions of components in the solutionfalling within the area A, C, B of FIGURE 1, said foam residing in saidsolution until reticulation has been effected, separating saidreticulated structure from said solution and stopping the reticulation.

10. In the alkali-catalyzed hydrolytic method for reticulatingpolyurethane foam to obtain a 3-dimensional reticulated structureconsisting of spaced-apart nexus and strands joined to said nexus andsubstantially free from membranous matter, the improvement comprising:submerging a membrane-containing polyurethane foam body in 20 parts ofsodium hydroxide per 100 parts of Water, benzyl alcohol and propyleneglycol reticulating reaction causing solution, the proportions ofcomponents in the solution falling within the area A, B and C of FIGURE2, said foam residing in said solution until reticulation has beeneffected, separating said reticulated structure from said solution andarresting the reticulating reaction.

References Cited UNITED STATES PATENTS 3,125,541 3/1964 H wa et al.260--2.5 x 3,125,542 3/1964 Haines 2602.5 x 3,171,320 3/1965 VOlZ 260-25x 3,322,701 5/1967 Bauer et a1. 2602.5 x

DONALD E. CZAJA, Primary Examiner.

M. J. WELSH, Assistant Examiner.

U.S. Cl. X.R.

